As is known, the body of motor vehicles is designed to obtain adequate safety for the passengers in the event of accidents. In particular, to sustain the load due to front crashes, longitudinal struts are provided in the front engine compartment of the motor vehicles, the struts having collapsible zones for absorbing energy.
Generally, the front end of the motor vehicle is supported by two main struts and by two lower struts, arranged under the main struts. The rear ends of the two lower struts are connected by a cross member, which supports the front suspensions and the powertrain (defined by the engine and by the gearbox of the motor vehicle).
In the event of front crash at a high speed, there is a need for the powertrain to deform the structure defining the passenger compartment as little as possible, to prevent injuries to the legs of the driver and front passenger in the motor vehicle. There is also a need to minimize the deceleration for the occupants in the passenger compartment. To meet these needs, normally a release system of pyrotechnic type is provided which, in the event of a crash, explodes and causes the release of the cross member, so as to let the powertrain fall.
The need is felt to simplify the solutions of the type described above, by eliminating the pyrotechnic devices for uncoupling the cross member.
Patent EP1361099, which corresponds to the preamble of claim 1, describes a sub-frame which is arranged under the two main struts and which comprises two longitudinal elements, a front cross member and a rear cross member. The two longitudinal elements have a notch which promotes downwards bending thereof when the front end of the motor vehicle is subjected to a front crash of a greater entity than a given threshold. The powertrain is supported by two lateral connection members, each of which is fixed, at the top, to a main strut and, bottomly to a longitudinal element of the sub-frame. The two connection members in EP1361099 have a notch which determines the breaking thereof when the load reaches a specific threshold during the bending of the longitudinal elements of the sub-frame, so as to uncouple the powertrain from the main struts.
The powertrain thus remains constrained only to the sub-frame, which, by bending, moves downwards and drags the powertrain with it.
The drawback of this solution lies in the fact that powertrain assembly is forced to move back together with the sub-frame, during the plastic deformation of the latter, hence there is a risk that it may in any event crash and deform the structure defining the passenger compartment.